Poisoned Attacks is all around excellent, just passing dice, even if only a few, through directly from hit to armour save with no drawbacks (since we have no Killing Blow or something which requires a to-wound roll) is def worth 35pts on its own.
For me the question is what other banners is the Spider Banner preventing me from taking. (And to be clear, it is for sure one of the five I’d always consider taking) The +1 to WS and Combat Resolution from the Big Red Raggedy Flag seems to be the better choice for me, as that jump to WS5 is a crucial step to be en par with elite units, so it helps both on offense as well as defense, while the combat res can be pivotal in ensuring your Black Orcs win the combat and/or stick around, especially if it’s a smaller unit and they’re punching above their weight class. The other banner which I find very very enticing is the Waaagh Banner. With Furious Charge and Choppas, Black Orcs truly shine when they charge, so giving them that edge to completing that charge can mean they can reach their full potential.